Han Yubing

Proof of a simple formula for ICI caused by single frequency offset in wireless OFDM system

Exact interchannel interference (ICI) expression caused by single frequency offset (SFO) is shown to be a function of normalized SFO (NSFO). Due to its high complexity, it is inconvenient for communication engineer to use this expression to calculate ICI value. Some upper bounds ICI, such as Moose and Feng, has been derived to reduce computational amount. But, they are still about 2 dB difference from real ICI value. Fortunately, this real ICI is proved to equal a third of the square of NSFO from mathematics under the condition that NSFO is small and N large. Numerical simulation further indicates that this identity holds when |NSFO|les0.2.

Threshold-based ML Channel Estimation for OFDM System in Sparse Wireless Channel

A joint maximum likelihood (ML) estimator, computing both channel impulse response (CIR) and noise variance , is proposed . Then, an adaptive threshold, defined as a linear function of the square root of noise variance, is introduced into this estimator. It can effectively filter channel noise over those weaker paths of the estimated CIR such that the entire performance of channel estimator can be further improved. This new ML channel estimator with threshold is called as the improved ML (IML) channel estimator. The simulated results in high and medium frequency channels show that the IML estimator obtains 1.5-2 dB SNR improvement over traditional ML for realizing the same bit error ratio (BER, <0.1), and achieves approximately the same BER performance as linear minimum mean square error (LMMSE) by using the lowest computational amount. This makes it very attractive for OFDM system in sparse wireless channel.